The present invention relates to a semiconductor nonvolatile memory and, in particular, to a recording device using a phase change material.
An example of a nonvolatile memory using a phase change film is described in detail in U.S. Pat. No. 5,883,827. This nonvolatile memory is a phase change memory in which a crystalline state of a memory element changes according to Joule heat (i.e., heat energy) caused by a current passing in the memory element itself and memory information is thereby written. As the temperature is caused to exceed 600° C. by the Joule heat and thereby melting a recording layer once when becoming amorphous, a resistance value of the memory element is changed by two to three digits according to the crystalline state, although its write current is high. This memory uses the resistance value as a signal, and so a read signal is large and sense operation is easy.
FIG. 2 shows a schematic diagram of a configuration of the phase change memory in FIG. 12 of U.S. Pat. No. 5,883,827. The phase change memory is comprised of a memory array, a row decoder XDEC, a column decoder YDEC, a read circuit RC and a write circuit WC. The memory array has a memory cell MCpr (p′=0, 1, . . . n, r=0, 1, . . . m) placed at each intersection of a word line WLp (p=1, . . . , n) and a data line DLr (r=1, . . . , m). Each memory cell has a memory element RM and a select transistor QM connected in series inserted between a data line DL and a ground potential. A word line WL is connected to a gate of the select transistor, and a column select line YSr (r=1, . . . , m) is connected to a corresponding column select switch Qar, respectively.
According to such a configuration, the select transistor on the word line selected by the row decoder XDEC conducts, and the column select switch corresponding to the column select line selected by the column decoder YDEC also conducts. A current path is thereby formed in a selected memory cell so that a read signal is generated on a common data line I/O. The resistance value in the selected memory cell is different depending on the memory information, and so the voltage outputted to the common data line I/O is different depending on the memory information. This difference is determined by the read circuit RC which reads the memory information of the selected memory cell.
JP-A-2001-502848 (corresponding to U.S. Pat. No. 5,825,046) describes a memory material including a transition metal element as the memory material used for an electrical memory element. According to a definition in the past, the transition metal element does not include a metal from the 2b group (of the Periodic Table of Elements) in many cases. However, the specification defines those up to the 2b group as the transition metal elements. An embodiment thereof describes a Ge—Sb—Te material as including Ti of less than 10 atom percent and so on.